Mastering time: Correct use of years and time spans
Using time references correctly can make your writing more precise and professional. Here’s a quick overview of how to write years and time spans properly in English.
Decades – avoid the apostrophe mistake
When referring to decades, don’t use an apostrophe before the final s.
Incorrect:
- 1980's
- 2000's
Correct:
- 1980s
- 2000s
Centuries – spell them out in running text
In academic and formal writing, centuries should be written out in words, especially in running text. Numerical forms may be used in tables, summaries or highly technical documents.
Incorrect:
- 20th century inventions changed everything.
Correct:
- The twentieth century saw rapid technological progress.
Starting sentences – never begin with a numeral
Generally avoid beginning a sentence with a numeral. Instead, spell out the number or rephrase the sentence (see also our language tip on numbers).
Incorrect:
- 30 startups participated in the accelerator programme focused on green tech.
Correct:
- Thirty startups participated in the accelerator programme focused on green tech.
Time spans – Use an en dash and full year formats
When indicating time spans in English, use an en dash (–), not a hyphen (-), with no spaces around it. In running text, it is generally best to write out the full years and avoid abbreviations.
Incorrect:
- 2001 - 2009
- From 2010–20, digital platforms transformed business models across industries.
Correct:
- 2001–2009
- From 2010 to 2020, digital platforms transformed business models across industries.
Note: In Danish, a hyphen is used with no spaces between years: 2001-2009.